The present disclosure relates to an image forming apparatus. More particularly, the present disclosure relates to a technique for adjusting a timing of secondary sheet feeding by a pair of registration rollers.
In a technique employed in image forming apparatuses such as copiers and printers, a pair of registration rollers feeds recording paper to a transfer point as secondary sheet feeding. The pair of registration rollers is disposed upstream of the transfer point in terms of a recording paper conveyance direction. Δt the transfer point, a toner image is transferred onto the recording paper by a photosensitive drum and a transfer roller. The pair of registration rollers adjusts a timing of conveyance of the recording paper to the transfer point. Specifically, the pair of registration rollers suspends temporarily conveyance of the recording paper, and then feeds the recording paper to the transfer point. The pair of registration rollers corrects skew of the recording paper. In the skew correction, a registration sensor detects the time when the recording paper arrives at the pair of registration rollers. The control section uses the time for controlling a starting timing of the secondary sheet feeding by the pair of registration rollers. The registration sensor is disposed in the vicinity of the pair of registration rollers.
In secondary sheet feeding by a pair of registration rollers in a general image forming apparatus, an upstream roller is rotated while a pair of registration rollers is in a suspended state. The upstream roller is located upstream of the pair of registration rollers in terms of a recording paper conveyance direction. The rotation of the upstream roller causes flexing of the recording paper. A high-speed apparatus resumes rotation of the pair of registration rollers at a starting timing of the secondary sheet feeding after the formation of the flexing of the recording paper. However, the rotational speed of the pair of registration rollers is different from the rotational speed of the upstream roller. The rotation of the upstream roller is therefore suspended. Then, the rotation of the pair of registration rollers and the rotation of the upstream roller need to be synchronized. Suspending the rotation of the upstream roller takes some time. Resuming the rotation of the upstream roller also takes some time. Consequently, the productivity desired for the image forming apparatus (the number of printed A4 recording paper sheets per minute: PPM) may not be achieved.
Some image forming apparatuses cause flexing of recording paper being fed to a conveyance belt without suspending rotation of the conveyance belt for conveyance of the recording paper.